How to encode protocol buffer string to binary using protoc - protoc

Question

I been trying to encode strings using protoc cli utility.
Noticed that output still contains plain text.
What am i doing wrong?
osboxes#osboxes:~/proto/bin$ cat ./teststring.proto
syntax = "proto2";
message Test2 {
optional string b = 2;
}
echo b:\"my_testing_string\"|./protoc --encode Test2 teststring.proto>result.out
result.out contains:
^R^Qmy_testing_string
protoc versions libprotoc 3.6.0 and libprotoc 2.5.0

Answer 1

Just to formalize in an answer:
The command as written should be fine; the output is protobuf binary - it just resembles text because protobuf uses utf-8 to encode strings, and your content is dominated by a string. However, despite this: the file isn't actually text, and you should usually use a hex viewer or similar if you need to inspect it.
If you want to understand the internals of a file, https://protogen.marcgravell.com/decode is a good resource - it rips an input file or hex string following the protocol rules, and tells you what each byte means (field headers, length prefixes, payloads, etc).
I'm guessing your file is actually:
(hex) 10 11 6D 79 5F etc
i.e. 0x10 = "field 2, length prefixed", 0x11 = 17 (the payload length, encoded as varint), then "my_testing_string" encoded as 17 bytes of UTF8.

Answer 2

protoc --proto_path=${protobuf_path} --encode=${protobuf_message} ${protobuf_file} < ${source_file} > ${output_file}
and in this case:
protoc --proto_path=~/proto/bin --encode="Test2" ~/proto/bin/teststring.proto < ${source.txt} > ./output.bin
or:
cat b:\"my_testing_string\" | protoc --proto_path=~/proto/bin --encode="Test2" ~/proto/bin/teststring.proto > ./output.bin